When constructing a well, and/or during certain wellbore operations, such as production, injection, intervention or the like, it may be necessary to provide a seal around a tubular in the well, such as to seal an annulus between the tubular and a bore wall. For example, during production of hydrocarbons from a subterranean reservoir, subterranean water may prematurely break through in certain regions of the associated wellbore, or water may cross over from a water injection well to an oil producing well. Such water breakthrough is highly undesirable and measures are normally taken to isolate any effected regions to minimise the volume of water being produced to surface. A well may pass through a porous rock formation, known as a “thief zone” into which injected water or other fluids may be lost, and it is desirable to seal such thief zones. Water breakthrough or fluid loss may also occur as a consequence of natural or artificial fractures, or fracture swarms. Further, in some instances the integrity of cement between a tubular, such as casing, and a bore wall may be compromised, for example due to a poor initial cement job, due to the formation of voids such as micro-annuli and the like. In such circumstances it may be desirable to perform a cement squeeze operation, in which cement, or other appropriate sealing medium, is used to fill such voids.
It is known to provide a seal around a tubular by injecting sealant around the tubular. This may require perforation of the tubular and injection of sealant sufficient to provide a seal. However, sealant can be lost following injection, for example by passing into an adjacent porous or fractured rock formation, by being flushed from the target site, for example, by a cross flow, or the like. It can therefore be difficult to determine how much sealant is required, and whether or not this has been deployed to establish a desired seal. Some circumstances may require the injection of a considerable volume (for example, several hundred liters) of sealant in order to ensure isolation or to increase the chances of establishing an appropriate seal, for example to seal a large annulus or to seal a length of an annulus sufficient to extend across a fracture swarm or isolate a rock formation from fluid pressure in order to prevent further fractures formation. Therefore, several trips downhole may be required, and/or complex systems may need to be utilised.